As someone who has laid out entire 2-300 page books in Word and LibreOffice both, what you say is a fine idea in theory, but rarely ever works out in actual app

As someone who has laid out entire 2-300 page books in Word and LibreOffice both, what you say is a fine idea in theory, but rarely ever works out in actual application at all with the way those tools implement it. I think LyX/LaTeX presents a saner hybrid here: using styles, yes, but also declarative markup for where to use those styles in the stream. This is far more analogous to how CSS is actually used (ie. in concert with HTML and being auto-applied to standard HTML tags), than how it ever works out in the mainstream tools available.